NBSIR 80-2079

An Economic Analysis of

Efficiency Improvements to

Residential Gas- and Oil-Fired

Central Heating Equipment

Stephen R. Petersen

Building Economics and Regulatory Technology Division

George E. Kelly

Building Equipment Division

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

U S. Department of Commerce

Washington, D C. 20234

July 1980

—Q0

100

.1156

80-2079

1980

c.2

Sponsored by

The Department of Energy

Washington, D.C. 20461

NATIONAL STANDARDS ^ XdDRi*xi^

NBSIR 80-2079

AN ECONOMIC ANALYSIS OF

EFFICIENCY IMPROVEMENTS TO

RESIDENTIAL GAS- AND OIL-FIRED

CENTRAL HEATING EQUIPMENT

Stephen R. Petersen

Building Economics and Regulatory Technology Division

BUG 1 2 1980

' ac

loo

USio

George E. Kelly

Building Equipment Division

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

U.S. Department of Commerce

Washington, D.C. 20234

July 1980

Sponsored by

The Department of Energy

Washington, D.C. 20461

U.S. DEPARTMENT OF COMMERCE, Philip M. Klutznick, Secretary

Luther H. Hodges, Jr., Deputy Secretary

Jordan J. Baruch, Assistant Secretary for Productivity. Technology, and Innovation

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

ABSTRACT

Minimum performance standards for new residential gas- and oil-fired furnaces

and boilers will be promulgated by the Department of Energy in the early

1980’s. These standards will implicitly require that a number of design

modifications be made to improve the seasonal efficiency of many basic

furnace/boiler configurations. This report examines the potential improvement in seasonal efficiency due to a number of such modifications, as well as their life-cycle cost effectiveness. Included in the analysis are intermittent ignition devices (for gas-fired equipment), improved heat exchangers,

stack dampers, external venting (with preheated air), and improved blower

motor efficiencies (for forced-air furnaces). Simulated furnace performance

data, the DoE/NBS furnace and boiler test procedures, recent estimates of

modification costs, and a wide range of annual heating requirements and fuel

costs are used in the analysis. The intermittent ignition device and improved

blower motor were found to be cost effective on all gas -fired furnaces. The

improved heat exchanger was cost effective for all new gas- and oil-fired

equipment. The stack damper and external venting modifications were found to

be cost effective for indoor equipment only in installations where substantial

annual heating requirements are prevelant. Minimum efficiency criteria for new furnaces and boilers are developed, based on the estimated performance

of current configurations representative of lower efficiency models, upgraded

with those energy-saving modifications which are generally cost effective and

can be implemented without serious disruption in the industry.

iii
PREFACE

< The work in this report has been conducted as an interdisciplinary research

project by the Building Economics and Regulatory Technology Division and

the Building Equipment Division within the Center for Building Technology,

National Engineering Laboratory, at the National Bureau of Standards. This

effort has been supported by the Consumer Product Efficiency Branch in the

Office of Buildings and Community Systems, at the U.S. Department of Energy.

The methodology outlined in this report employs a parametric analysis technique. The numerical values resulting from this analysis are valid only for

the set of parameters specified. The NBS analysis and selection of parameters

covers only a few of the many factors that DoE is required by law to consider

in setting minimum efficiency standards.

ji

iv
TABLE OF CONTENTS

Page

ABSTRACT iii

PREFACE iv

LIST OF TABLES vi

LIST OF FIGURES vii

SI CONVERSIONS viii

EXECUTIVE SUMMARY ix

1. INTRODUCTION 1 2. NEED FOR ECONOMIC ANALYSIS IN MINIMUM STANDARDS

DEVELOPMENT 1 3. EQUIPMENT DESIGN MODIFICATIONS AND CORRESPONDING

SEASONAL EFFICIENCIES 3

3.1 Modifications Considered 3

3.2 Estimating Improvements in Seasonal Efficiency Due to

Design Modifications 3

3.3 Estimating the Relative Cost Effectiveness of Design

Modifications 6

4. CALCULATION OF ANNUAL ENERGY SAVINGS AND LIFE-CYCLE COSTS 10

4.1 Calculating Annual Energy Requirements and Annual Energy

Costs for a Furnace or Boiler 10

4.2 Estimating Annual Heating Requirements and Design

Heating Loads 13

4.3 Calculation of Annual Energy Savings 1 !'/ 4.4 Life-Cycle Cost Analysis of Design Modifications 21

4.4.1 Calculation Procedures 21

4.4.2 Economic Assumptions Used in Analysis 22

4.4.3 Results of Life-Cycle Cost Analysis 23

4.4.4 Implications for Outdoor Furnaces and Boilers 28

5. IMPLICATIONS FOR STANDARDS DEVELOPMENT 29

5.1 An Economically Optimal Standard for Consumers 29

5.2 A Practical Standard for Manufacturers 29

5.3 Other Considerations in Setting Standards for Furnaces

and Boilers 30

5.4 Technical Basis for Standards Setting 33

5.4.1 Gas Furnaces and Boilers 33

5.4.2 Oil Furnaces and Boilers 34

6. AN ALTERNATIVE METHOD FOR SPECIFYING MINIMUM BLOWER MOTOR

EFFICIENCY 36

7. CONCLUSIONS 36

v
TABLE OF CONTENTS (continued)

Page

REFERENCES 40

APPENDIX A. Derivation of Modified Uniform Present

Worth Factors A-l

APPENDIX B. Explanation of Design Modifications to

Furnace/Boilers B-l

LIST OF TABLES

1. Design Modifications to Improve the Performance of New Gasand Oil-Fired Furnaces and Boilers 4

2. Seasonal Efficiency of Selected Gas-Fired Furnace/Boiler

Configurations Located Indoors 5

3. Seasonal Efficiency of Selected Oil-Fired Furnace/Boiler

Configurations Located Indoors 7

4. Relative Savings-Cost Ratios for Selected Modifications to

Gas-Fired Furnaces/Boilers Located Indoors 8

5. Relative Savings-Cost Ratios for Selected Modifications to

Oil-Fired Furnaces/Boilers Located Indoors 9

6. Annual Heating Hours Calculated for 1200 sq. ft. House in

Selected Locations 14

7. Annual Heating Requirements, Design Heating Loads and Annual

Heating Hours Used in Thermal Analysis 18

8. Annual Energy Savings by Modification for a Gas Furnace with

Electric Blower 19

9. Annual Energy Savings by Modification for an Oil Furnace with

Electric Blower . 20

10. Minimum Annual Heating Requirements (in million Btu) for

Cost-Effective Modifications, Gas Furnace 25

11. Minimum Annual Heating Requirements (in million Btu) for

Cost-Effective Modifications, Oil Furnace 26

12. Furnace/Boiler Output Capacities Corresponding to Annual

Heating Requirements 31

vi
LIST OF TABLES (continued)

Page

13. Minimum Seasonal Efficiencies for Gas-Fired Central Heating

Equipment 34

14. Minimum Seasonal Efficiencies for Oil-Fired Central Heating

Equipment 35

15. Minimum Efficiencies for Furnace Blower Motors 36

LIST OF FIGURES

1. Annual Heating Requirements as a Function of Design Heating

Loads (1200 sq. ft. house) 15

2. Relationship Between Design Heating Load and Corresponding

Minimum Annual Heating Requirements 16

3. Typical P.S.C. and S.P. Motor Efficiencies and Suggested

Minimum Motor Efficiency Level 37

vii
SI CONVERSIONS

Because the energy analysis in this report is based directly on the Department of Energy Test Procedure for Furnaces and Boilers and is directly

supportive to the DoE effort to develop minimum performance standards for

furnaces and boilers, compatable customary units of measurement are used.

Since the United States is a signatory to the Eleventh General Conference on

Weights and Measures, which defined and gave official status to the Metric

SI system, the following conversion factors are provided to assist users of

SI units.

Energy: 1 Btu = 1.055 x 10^ joule

Power: 1 Btu = 0.293 watt

1 hp = 0.7450 kW

Temperature: 1 °F = 9/5°C +32

Length: 1 foot = 0.3048 meter

viii
EXECUTIVE SUMMARY

This report provides a microeconomic analysis of selected design modifications to residential furnaces and boilers in order to generate benchmark data

for the development of minimum performance standards for new furnaces and

boilers by the Department of Energy. These minimum performance standards

will pertain to residential gas and oil-fired forced warm-air furnaces with

heat input rates less than 225,000 Btu per hour (Btu/h) and residential gasand oil-fired, hot water and steam boilers with heat input rates less than

300,000 Btu per hour.

A number of design modifications to improve the seasonal energy efficiency of

new furnaces and boilers are examined in this report. These include:

° automatic stack damper,

0 intermittent ignition device,

0 direct venting with preheated air,

° improved heat exchanger, and

° high efficiency blower motor.

Detailed calculations of annual energy savings attributable to each of these

modifications are made. Life-cycle dollar savings are then calculated for

each modification and compared with corresponding costs in order to determine

the cost effectiveness to the end user. Other factors relevant to the development of minimum performance standards are also examined, including the

acceptable performance of the modification considered and their potential for

large-scale disruption to the producing industries.

A useful furnace life of twenty years and a real discount rate (i.e., after

adjusting for inflation) of four percent were used in a life-cycle cost

analysis of the modifications. Base year energy costs of $0.30 per therm for

natural gas, $1.00 per gallon for fuel oil, and $0.04 per kWh for electricity

were also used, with a sensitivity analysis performed to examine the effects

of this factor on the cost effectiveness of the modifications examined.

Energy and dollar savings were calculated for annual heating requirements

(AHR) of a house ranging from five to eighty million Btu. Except for the

intermittent ignition device, which appears to be cost effective in nearly

all cases, the savings attributable to the modifications considered are

approximately proportional to AHR. Thus, while some of the modifications

are not cost effective in relatively small or tightly insulated houses in the

milder climates (e.g., stack damper and direct venting with preheated air),

they are all likely to be cost effective in larger houses in the colder climates. Since the furnace/boiler size is likely to be larger in houses with

larger AHR than in those with relatively small AHR, this report suggests that

a minimum efficiency standard would require a higher level of efficiency for

a larger furnace/boiler than for a smaller sized unit.

Two important constraints are identified that tend to reduce potential minimum efficiency requirements below levels that are shown to be cost effective

in this report:

ix
(1) stack dampers on oil-fired furnaces and boilers have been

associated with odor problems, and

(2) the requirement that all new furnaces include direct venting

with preheated air would place a severe redesigning burden

on the industry.

In addition, the improved blower motor efficiency for furnaces, which is

shown to be cost effective for gas furnaces only, cannot be factored into

the minimum seasonal efficiency requirements directly. Thus the blower

motor efficiency level must be specified independently of the fuelutilization efficiency if higher motor efficiencies are to be required.

Based on the economic analysis and constraints identified in this report,

the following seasonal efficiencies appear to be a reasonable starting

point for developing minimum efficiency standards for new furnaces and

boilers:

Heating Equipment Type

Gas Oil

Indoor furnaces and

indoor boilers with

output capacities

< 40,000 Btu/h 60% 76%

Indoor furnaces and

indoor boilers with

output capacities

> 40,000 Btu/h 74% 76%

Outdoor furnaces and

outdoor boilers 64% 73%

x
1 . INTRODUCTION

This report provides a microeconomic analysis of selected design modifications to residential furnaces and boilers in order to generate benchmark

data for the development of minimum performance standards for new furnaces

and boilers by the Department of Energy. These minimum performance standards

will pertain to residential gas and oil-fired forced warm-air furnaces with

heat input rates less than 225,000 Btu per hour and residential gas- and oilfired, hot water and steam boilers with heat input rates less than 300,000

Btu per hour.

The development of minimum performance standards is required by the National

Energy Act of 1978 and is the responsibility of the Department of Energy

(DoE). The National Bureau of Standards (NBS) has been requested by the

Department of Energy to assist in this endeavor by providing a technical and

economic analysis of the various design options likely to be cost effective

for residential furnaces and boilers. This report summarizes the economic

analysis pertaining to this NBS effort and provides both a methodology and

data relevant to the development of such minimum performance standards.

A number of design modifications to improve the seasonal energy efficiency of new furnaces and boilers are examined in this report. Detailed calculations

of annual energy savings attributable to each modification are made, based on

the DoE furnace/boiler test procedures [5] developed at NBS. Life-cycle dollar savings are then calculated for each modification and compared with cor- responding costs in order to determine the cost effectiveness to the end user. Other factors relevant to the development of minimum performance standards

are also examined, including the acceptable performance of the modifications

considered and their potential for large-scale disruption to the producing

industries

This report does not reflect a position for or against the promulgation of

minimum furnace and boiler standards. Rather, given that such standards are legislatively mandated, the purpose is to promote the development of minimum

standards that can be realistically implemented and which are economically

justified.

2. NEED FOR ECONOMIC ANALYSIS IN MINIMUM STANDARDS DEVELOPMENT

Several major criteria have been established by the Department of Energy for

consideration in the development of minimum performance standards for fur- naces and boilers [4]. These have been interpreted to provide the following

constraints on the minimum standards development process:

1. The standards must be stated in terms of a minimum acceptable level

of seasonal efficiency, as demonstrated by the DoE test procedure

[5],

2. The standards must be technically feasible,

1
3. The standards must be achievable without a major disruption of the

industries manufacturing the appliances,

4. The standards must not be set at a level which will force unsafe,

unreliable or unacceptable products on the consumer, and

5. The standards must be capable of being met with product and design

changes which are "cost effective."

It is this last criterion that is most subjective and which has many interpretations. Should the design changes resulting from the minimum standard be

cost effective everywhere in the country or just for average installation

conditions in the country? Should there be different minimum standards for

different geographical regions? For different heating requirements? For

different energy prices? One way to answer these questions is through an economic analysis which evaluates the design changes in terms of their impact

on life-cycle costs, over a wide range of applications. If such an analysis

is made a part of the minimum standards development process, it has the additional benefit of encouraging standards which are consistent with existing

economic incentives and thus are likely to be implemented with a minimum of

enforcement costs.

The type of minimum performance standard that is most likely to be promulgated by DoE is a single standard imposed at the point of manufacture. This

is because residential furnaces and boilers are manufactured at a central

location, often sold through distributors or retailers, and usually not subjected to major modification at the installation site. Such a single standard, however, is basically inconsistent with the concept of economic efficiency. That is, a single standard is likely to require too much investment

in energy efficiency in installations with low annual heating costs and too

little investment in energy efficiency in installations with relatively high

heating costs. A more flexible standard which requires a level of energy

efficiency that varies with annual heating requirements and energy prices

would save more energy dollars for the same total investment cost, or the same level of energy dollars at a lower total investment cost. Such an alternative standard would also be more consistent with existing economic

incentives to install more efficient heating equipment in colder climates, in

larger buildings, or where higher fuel prices prevail.

Because the single-standard approach has been favored by DoE, however, the

scope of this report is limited to an analysis of a single standard imposed

at the point of manufacture and not differentiated by geographic region. As

a result, it is assumed that the major purpose of such a standard would be to

eliminate production models which fail to achieve the minimum level of energy

efficiency which can be economically justified in most, if not all installations in the United States. Alternative mechanisms, including market forces

(e.g., fuel costs), information programs (e.g., appliance labeling), and tax

credits, would provide incentives to exceed such a level, where economically

justified. For this reason, the thrust of this report will be to identify

the design options for several furnaces and boilers that can be shown to be

cost effective in most conventional installations on a life-cycle basis.

2
3. EQUIPMENT DESIGN MODIFICATIONS AND CORRESPONDING SEASONAL EFFICIENCIES

3.1 MODIFICATIONS CONSIDERED

A number of modifications can be incorporated into the design of fossil-fuelburning heating equipment in order to improve seasonal energy utilization

efficiency. Modifications which are either presently available or likely to

be available in the very near future are listed in table 1, together with

their additional purchase cost to the consumer in 1980 dollars, as estimated

by Booz , Allen, and Hamilton [1]. A short description of each of these

modifications is presented in Appendix B.

All but one of the modifications listed in table 1 improve the seasonal

fossil-fuel utilization efficiency of the heating equipment. The high efficiency blower motor does not affect fossil-fuel utilization efficiency but

does decrease the amount of electricity needed to operate the system.

Fossil-fuel utilization and electricity utilization are kept separate in

order to reflect the significantly different prices of these two energy types.

Dollar valuations of the two energy types are added together in order to

arrive at a total operating cost. Except when referring specifically to

blower motor efficiency, the term "efficiency" or "seasonal efficiency" will

refer to fossil fuel utilization efficiency.

Power burners for gas-fired systems and fuel/air modulation modifications

for both gas- and oil-fired systems were eliminated from the economic analysis for the following reasons. While a power burner is standard on oilburning equipment, the use of a stack damper on a gas-fired unit provides

most of the same benefits in reducing off -period flue losses, costs roughly

the same as a power burner, uses significantly less electrical energy, and

has the important advantage of not requiring a major redesign of a furnace

or boiler. The fuel/air modulation modification has the highest first cost

of all the modifications considered and provides little increase in seasonal

efficiency once a vent damper and intermittent ignition device (IID) are installed to reduce off-cycle losses.

3.2 ESTIMATING IMPROVEMENTS IN SEASONAL EFFICIENCY DUE TO DESIGN MODIFICATIONS

Annual energy usage and energy savings due to improvements in heating equipment design are a function of seasonal efficiency rather than a steady-state

efficiency. Although the improvements in seasonal efficiency associated with

many of the modifications in table 1 have been estimated in a number of

reports [1,3,10], an (unpublished) in-house NBS study, using the NBS computer

model DEPAF, Design and Performance Analysis of Furnaces [3], appears to

provide the most complete and internally consistent analysis of furnace and

boiler design options. This study was performed for the Department of Energy

for the purpose of setting efficiency targets. It involves the analysis of

furnace/boiler performance in several geographic locations and covers all of

the design options (and many of their combinations) listed in table 1.

Table 2 summarizes the results of this NBS study for a high efficiency gasfired furnace or boiler, having a steady-state efficiency of 77 percent, in

3
Table 1. Design Modifications to Improve the Performance of New Gasand Oil-fired Furnaces and Boilers

Application3

Symbol Design Option Oil Gas

Approximate

Cost (1980) b

P Power Burner S X $120

F Fuel and Air Modulation X X 150

S Automatic Stack Damper X X 3 25

I Intermittent Ignition Device (IID) S X 75

VX Direct Venting with Preheated Air X X 85

E Improved Heat Exchanger

(5 percentage points

improvement in

X X 25

B High Efficiency Blower Motor

(P.S.C.d instead of Shaded Pole)

X X 10

a

S = X = standard equipment.

design option either presently available or likely to be available

shortly.

b Source: Booz , Allen & Hamilton, Inc., Energy Efficiency Program for

Appliances, Furnaces, Home Heating Equipment, Humidifiers , Oct. 1977 [1].

Q T] sS = steady-state efficiency of furnace or boiler, based on DoE test

procedures [ 5

]

^ P.S.C. = permanent-split capacitor.

4
Table

2.

Seasonal

Efficiency

of

Selected

Gas-Fired

Furnace/Boiler

Configurations

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three geographic locations and for the design options of interest. Similarly,

DEPAF results for a high efficiency oil-fired furnace or boiler with a steady-state efficiency of 83 percent are shown in table 3. The symbols used

to identify each design variation are shown in table 1.

Also shown in tables 2 and 3 are estimated seasonal efficiencies for gas- and

oil-fired units, respectively, having steady-state efficiencies of 72 percent.

These latter numbers were generated by adjusting the DEPAF computer results

downward to give seasonal efficiencies which are representative of poorer

performing units having more massive heat exchangers, while maintaining the same relative seasonal efficiency trends for the different regions.

It should be pointed out that in all the design options presented in tables

2 and 3, an intermittent ignition device (I) is assumed to be installed.

This simplified approach was used since the economic analysis in this report

shows that the intermittent ignition device is almost always cost effective,

either alone or in combination with other modifications. Since we are primarily interested in incremental costs and incremental savings (see section

4), it is more meaningful to present the various design options as modifications to units already equipped with an intermittent ignition device.

This procedure provides an internally consistent set of data which is in close

agreement with the little data that are available on seasonal efficiencies

predicted by the DoE furnace test procedure [5] for some of the simple design

options. It also provides a set of data that is believed to bracket, on the

high and low side, the steady-state and seasonal performance of the majority

of gas- and oil-fired furnaces and boilers presently being marketed.

3 .3 ESTIMATING THE RELATIVE COST EFFECTIVENESS OF DESIGN MODIFICATIONS

Using the seasonal efficiency data in tables 2 and 3, the percentage reduction in annual fossil-fuel requirements due to the design modifications

examined can be calculated using:

1

_ _ Percent Fuel Savings = (100) —- — = (100) — — , _ n 2

n l

where and ri 2 are the seasonal efficiencies without and with the modification, respectively. The resulting savings (in percentage terms) can then be

divided by the cost gf the modification (from table 1) to obtain relative

savings-cost ratios. These relative savings-cost ratios show the percent

reduction in heating costs per dollar invested. They can be used to determine the most cost-effective order in which modifications should be made.

Tables 4 and 5 list the relative savings-cost ratios for selected combinaImplicit in this analysis is the assumption that each of the modifications has the same service life. Different service lives would

require an adjustment to cost.

6
Table

3.

Seasonal

Efficiency

of

Selected

Oil-Fired

Furnace/Boiler

Configurations

Located

Indoors

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value.
Table

4.

Relative

Savings-Cost

Ratios 3

for

Selected

Modifications

to

Gas-Fired

Furnaces/Boilers^

Located

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Relative

Savings-Cost

Ratios 3

For

Selected

Modifications

to

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Furnaces/Boilers^

Located

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tions of the stack damper (S), the improved heat exchanger (E) and direct

venting (with preheating of incoming air, VX), for gas- and oil-fired units,

respective ly

.

From tables 4 and 5 it is easily seen that the single modification to a gasor oil-fired unit which is most cost effective is the improved heat exchanger

(E). This modification is therefore considered first in the determination

of life-cycle savings in section 4. Once this modification has been made,

tables 4 and 5 show that the stack damper (S) is slightly more cost effective

than direct venting with preheating (VX) , except in the case of the highefficiency gas-fired furnace or boiler in the coldest of the three locations

(Syracuse). Based upon these results, and our belief that with mass production and design improvements the cost of the stack damper will decrease more

rapidly than a direct vent system, the stack damper is evaluated second in

the economic analysis which follows. This leaves direct venting with preheating of incoming combustion air as the last modification of these three

to be considered for implementation.

Given the relative cost effectiveness of the stack damper, improved heat

exchanger and direct venting with preheating, the absolute cost effectiveness

of these modifications can now be calculated. This requires an estimate of

the actual energy savings and a life-cycle cost valuation of those savings.

This is the subject of the next section.

4. CALCULATION OF ANNUAL ENERGY SAVINGS AND LIFE-CYCLE COSTS

This section covers four topics: computation procedures to determine annual

energy requirements and costs of operating a furnace or boiler; specification

of the annual heating requirements and design heating loads used in the

analysis; life-cycle cost procedures and assumptions; and discussion of the

results obtained from the engineering and economic analyses.

4.1 CALCULATING ANNUAL ENERGY REQUIREMENTS AND ANNUAL ENERGY COSTS

FOR A FURNACE OR BOILER

The Department of Energy has published testing and calculation procedures for

determining the seasonal performance of residential central furnaces and

boilers [5], based on an NBS research report for this purpose [9]. These

procedures provide a methodology for computing the number of burner operating

hours (BOH) and the annual energy costs (AEC) for a given size furnace in a given house and climate. This methodology is used in this report to calculate the annual energy and dollar savings for the design modifications examined. However, instead of using design heating requirements (DHR) and heat-

* The design heating requirement is the heating requirement to be met by the

furnace or boiler in Btu per hour at the 97-1/2 percent outdoor design

temperature.

10
ing load hours (HLH) to determine the annual heating requirements (AHR) of

different structures, as in the recommended test procedure, the annual heating requirements are specified directly in the analysis.

Based on the DoE/NBS test procedure, the annual number of burner operating

hours (BOH) for a furnace or boiler may be calculated using the following

equation:

AHR - (AHH) (Q ) (n ) Tj0U = tr _ (3413) (PE + yBE) + (Qln - Q

p

)(nu) (4-1)

where AHR = the annual heating requirement, in Btu, of the residence in

which the furnace or boiler is to be installed,

AHH = annual heating hours (i.e., the number of hours in which

the outdoor dry-bulb temperature falls below the balance

point temperature of the house),

fuel input rate to the furnace or boiler in Btu/h,

fuel input rate to the pilot in Btu/h,

a fraction representing the seasonal efficiency of the

furnace or boiler,

3413 = number of Btu in one kWh,

PE = power to burner (kW),

BE = power to furnace blower** (kW), and

y

= ratio of average blower on-time to average burner on-time

(assumed to be 1.38 for furnace, 1.0 for boiler or furnace

employing a single motor to drive a power burner and

blower)

.

Equation 4-1 accounts for the useful output from the pilot flame during heating hours and credits the unit with the heat output from the electric blower

and/or power burner when the equipment is operating. In the economic analysis which follows, it is assumed that the fuel input rate to the pilot on gas-fired units is 1000 Btu/h and that the blower employed uses a one-third

Heating load hours = 24 * Heating Degree DaXs (base ,6^ F) _ „he

AT re design

ATdesign

= 65°F - (97-1/2 percent outdoor design temperature).

The energy used by the pump motor on a hot water boiler is small and

is neglected in the analysis which follows.

11
horsepower motor. The blower design option consists of using a permanentsplit capacitor (P.S.C.) motor with an efficiency of 65 percent instead of a shaded pole (S.P.) motor with an efficiency of 45 percent.

For the purposes of this report the output capacity (Q^n x n ss ) of the

furnace/boiler is assumed to be 1.7 times the design heating load, where n gs

is the steady-state efficiency of the furnace or boiler. That is, the fur- ace or boiler is assumed to be 70 percent oversized. Oversizing of this magnitude is consistent with the need to provide a reasonably short warm-up

period after a thermostat setback. This is also the oversizing ratio used in

the furnace and boiler test procedures recommended by NBS and DoE.

Annual fuel consumption (AFC) and annual electricity consumption (AELC) can

then be calculated using:

(BOH) (Q in " Q ) + (8760) (Q ) AFC = —, and

Btu/unitp

(4-2)

AELC = (BOH) (PE + yBE) (4-3)

where 8760 = the number of hours in a year, and

Btu/unitp = the energy content in Btu per unit of fuel purchased

(e.g., gallon, therm).

The annual energy cost (AEC) is then:

AEC = (AFC) ($/unitF

) + (AELC) ($/kWh), (4-4)

where $/unitp = the price in dollars of a unit of fuel, and

$/kWh = the price in dollars of a kWh.

It is interesting to note that for a given furnace or boiler, an increase in

fuel utilization efficiency will reduce both fuel requirements and electricity requirements. Replacement of the pilot light will reduce annual fuel

requirements but increase BOH and thus increase annual electricity use by the

furnace blower and power burner (if any). Conversely, improvement in the

furnace blower motor or power burner will reduce electricity requirements but

increase fuel requirements. When neither a pilot light nor auxiliary electrical equipment exist, BOH and AFC are directly proportional to AHR.

Another important fact is that the energy savings due to the IID are inversely

related to annual heating hours (AHH) . That is, a greater number of AHH

* Note that the energy savings from the IID may be larger than calculated

by the above methodology if the standing pilot flame contributes to the

air conditioning load. However, this is ignored in the present study

because of the difficulty in generalizing this effect.

12
results In a shorter non-heating season, lower standby losses from the pilot

and, as a result, smaller savings from an intermittent ignition device. In

addition, the absolute value of the pilot losses are approximately constant

for a given value of AHH and Q . Thus any estimate of a seasonal fuel utilization efficiency which includis pilot losses changes as the annual heating

requirement (AHR) changes. This is part of the reason that the seasonal

efficiencies presented in tables 2 and 3 were only given for units equipped

with intermittent ignition devices.

In order to evaluate the change in energy requirements due to the IID, the

number of annual heating hours must be estimated for the actual building in

which the furnace/boiler is to be installed. AHH are, however, not only a function of climate, but a function of the balance point temperature of the

building as well. Recent NBS analysis of a 1200 sq. ft. house sequentially

modified to reduce heat losses [12] has shown that AHH vary significantly

with the thermal integrity of the shell. Table 6 provides the AHH for this

1200 sq. ft. house for several levels of thermal integrity and corresponding

balance points in 14 locations. The AHH corresponding to the approximate

level of insulation that is economically optimal in each location (as determined in [12] for fossil-fuel heating systems) are denoted by asterisks.

4.2 ESTIMATING ANNUAL HEATING REQUIREMENTS AND DESIGN HEATING LOADS

In order to calculate annual fuel and electricity consumption of a furnace or boiler using equations 4-1 through 4-3, some estimate of annual heating

requirements (AHR) is needed. Figure 1 provides quantitative data on AHR for

smaller single-family houses in the U.S. based on a recent NBS study [12].

The lines for each of the thirteen cities represented show the range of AHR

for the same basic 1200 sq. ft. single-story house with insulation levels

varying from nil (top end) to extreme by today's standards (bottom end). The

same lines also show the corresponding design heating loads for the identical

house configuration. This data is based on an hour-by-hour analysis using

test reference year (TRY) weather data [14], with thermostat settings at 68°F

during the day and 60°F at night. In general, the AHR for an appropriately

insulated 1200 sq. ft. house will be approximately one-third of the maximum

value shown (i.e., 1/3 of the AHR for the uninsulated house). According to

this data, AHR lower than five million Btu would appear reasonable only in

the mildest regions of the U.S. in houses with less than 1200 sq. ft., moderately well insulated and conservatively operated. A larger house or one operated less conservatively would have higher AHR.

Estimates of design heating loads (DHL) are also needed in order to determine

the proper furnace or boiler size for a given installation. (Output capacity

is assumed to be sized 1.7 times the DHL.) The data in figure 1 show that

there is a poor correlation between the design heating load (DHL) and annual

heating requirements as different locations are considered. For example, in

Phoenix, a DHL of 30,000 Btu/h corresponds to AHR of approximately 18 million

Btu, while in Seattle the same DHL corresponds to AHR of over 60 million Btu.

However, minimum AHR corresponding to DHL's at different levels can be established that will prove useful. Figure 2 provides a single curve, based on

13
Table 6. Annual Heating Hours (AHH) Calculated for 1200 sq. ft. House

in Selected Locations3

City

Balance Point Temperature, Heating ( °F)

58 55 53 50

Miami 200 100* 50 30

Phoenix 2100 1250* 900 650

San Antonio 2350 1750* 1450 1250

Fort Worth 2650 2000* 1600 1350

San Francisco 4950 3050* 2050 1350

Sacramento 5150 2900* 2250 1850

Atlanta 3200 2400 2000* 1750

Washington 4300 3550 3100* 2800

Seattle 6650 5650 4850* 4300

Kansas City 4300 3650 3300* 3050

Boston 5300 4600 4200 3900*

Chicago 5150 4550 4150* 3900

Madison 5700 5100 4700 4450*

Minneapolis 5500 5050 4750 4600*

3 Source, table 6.9 in [12].

Approximate balance point corresponding to economic level of

insulation for fossil-fuel heating system (based on 1200 sq. ft.

house)

*
Minneapolis

15

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000

Design

Heating

Load

(Btu/hour)

Figure

1.

Annual

heating

requirements

asa

function

of

design

heating

loads

(1200

sq.

ft.

house)
T T T T T

CO

03

3

bi)

E

ba

a>oo

to CO

*

00

a>o

o

CO

TO _o

bfl

CO03

JC * e co

bfl -g

00 «

a

« E

03

1 &

£ £

« bo jn 2?

•=C coQ)

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03 C

ac co

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03

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03 CO l» CO CM

Ima gOil siN3W3amo3a 9NUV3H ivdnnv

16
figure 1, which shows the approximate minimum AHR for any given value of DHL.

This curve is used to generate the DHL corresponding to the range of AHR (5 to

80 million Btu) examined in the following subsection. It will also be of some use in developing data for establishing minimum performance standards for

furnaces and boilers since the minimum AHR corresponding to any given furnace/

boiler size can be estimated. Table 7 provides the design heating loads and

annual heating hours that are assumed to correspond to each level of AHR examined in the range of 5 to 80 million Btu.

4.3 CALCULATION OF ANNUAL ENERGY SAVINGS

Tables 8 and 9 show the annual savings in fossil fuel and electricity estimated for the design improvements examined in this report, using the calculation methodology shown in section 4.1. Fossil fuel savings are shown in gallons (140,000 Btu/gallon) for oil and therms (100,000 Btu/therm) for natural

gas. For the intermittent ignition device (IID, gas-fired furnaces and boilers

only) the energy savings are calculated as a function of 2500, 3500, and 5000

annual heating hours. Calculation of savings for the IID are shown in part I of table 8. For all other modifications, savings are calculated as a function

of annual heating requirements (AHR) of 10, 20, 40 and 80 million Btu.

Calculations of savings from improvements in blower efficiency assume an increase in motor efficiency from 45 to 65 percent. Calculations of savings

for the improved heat exchanger, stack damper, and direct venting (with

preheat) are based on the seasonal efficiency data shown in tables 2 and 3

for Washington, D.C. This location was selected for the analysis because the

percentage savings are the most conservative of the three locations, and thus

provide an estimate of minimum savings to be expected. Energy savings shown

in part II of table 8 and part I of table 9 were calculated in the sequential

order shown, with the IID installed in all cases. (The sequential ordering is

based on diminishing savings-cost ratios.) Thus these calculations provide

the incremental savings from each additional modification as shown. Energy

savings in part III of table 8 and part II of table 9 were calculated for each

modification independently, although the IID is assumed to be used in all

cases.

Note that the savings in electricity due to the improved blower efficiency

require that more fossil fuel be burned in order to provide an equivalent Btu

output. (The "waste" heat from the blower is actually useful in terms of overall furnace output.) As a result, the improved blower efficiency will be

advantageous only if the Btu output from the fossil fuel is less costly (on a life-cycle cost basis) than the Btu output from the blower. Because natural

gas prices are significantly lower than heating oil prices (per Btu) the

improved blower efficiency modification is ranked higher in the sequential

analysis for the gas-fired systems than for the oil-fired systems.

This data base will be used for calculating the life-cycle savings from

furnace/boiler design modifications in the following sections.

17
Table 7. Annual Heating Requirements, Design Heating Loads and Annual

Heating Hours Used in Thermal Analysis

Annual Heating Design

Requirements (million Btu) Heating Load (1000 Btu)

Annual

Heating Hours

5 15.0 2000

10 22.5 2500

15 27.5 3000

20 32.5 3500

25 35.0 4000

30 40.0 4500

40 45.0 5000

50 50.0 5000

60 55.0 5000

80 60.0 5000

18
Table 8. Annual Energy Savings by Modification for a Gas Furnace with Electric

Blower

I. Intermittent Ignition Device (IID)

Annual Gas (Electricity) Savings in Therms (kWh)

Furnace Efficiency

Steady Seasonal

State (before modification)

Annual Heating Hours

(Annual Heating Requirements3

, million Btu)

2500 3500 5000 5000

(10) (20) (40) (80)

72% 62% 64.3 (-30.0) 54.2 (-29.6) 39.2 (-28.1) 38.8 (-21.6)

77% 69% 64.2 (-32.4) 54.2 (-31.9) 39.1 (-30.2) 38.8 (-23.4)

II. Sequential Analysis*1

Annual Gas (Electricity) Savings in Therms (kWh)

Annual Heating Requirements (million Btu)

A. T) = 72% 10 20 40 80

S S

' ' .. rfM .— -— — - - — " ' — — Improved Blower (h=65%) -3.4

Improved Heat Exchanger (5%) 6.7

Stack Damper 20.3

Direct Vent, (w/preheat) 4.6

B. n 77%

ss Improved Blower (D=65%) -3.0

Improved Heat Exchanger (5%) 5.5

Stack Damper 12.7

Direct Vent, (w/preheat) 4.1

III. Independent Analysis*5

A. n 72%

ss Improved Blower (h=65%) -3.4

Improved Heat Exchanger (5%) 6.7

Stack Damper 16.7

Direct Vent, (w/preheat) 8.8

B * n ss= 77 *

Improved Blower (D=65%) -3.0

Improved Heat Exchanger (5%) 5.5

Stack Damper 8.9

Direct Vent, (w/preheat) 7.2

a AHR correspond to values given in table

** IID assumed to be used in all cases.

(62.5) -5.0 (90.0) -6.6 (120.7) -11.2 (203.0)

(6.7) 13.9 (9.5) 28.4 (12.7) 57.2 (21.3)

(20.1) 41.7 (28.7) 85.3 (38.1) 171.9 (64.0)

(4.6) 9.4 (0.5) 19.2 (8.6) 38.7 (14.4)

(60.4) -4.3 (86.8) -5.8 (116.0) -9.7 (196.0)

(5.8) 11.3 (8.3) 23.1 (11.0) 46.5 (18.5)

(13.4) 26.0 (19.1) 53.2 (25.4) 107.2 (42.7)

(4.4) 8.5 (6.3) 17.4 (8.3) 35.0 (13.9)

(62.5) -5.0 (90.0) -6.6 (120.7) -11.2 (203.0)

(6.7) 13.9 (9.5) 28.4 (12.7) 57.2 (21.3)

(16.6) 34.4 (23.6) 70.4 (31.5) 141.9 (52.8)

(8.8) 18.2 (12.5) 37.3 (16.7) 75.2 (28.0)

(60.4) -4.3 (86.8) -5.8 (116.0) -9.7 (196.0)

(5.8) 11.3 (8.3) 23.1 (11.0) 46.5 (18.5)

(9.4) 18.3 (13.4) 37.4 (17.9) 75.4 (300.0)

(7.6) 14.8 (10.9) 30.4 (14.5) 61.2 (24.4)

7 for indicated annual heating hours.

19
II.

III.

Table 9. Annual Energy Savings by Modification for an Oil Furnace with Electric

Blower

Sequential Analysis Annual Oil (Electricity) Savings in Gallons (kWh)

Annual Heating Requirements (million Btu)

10 20 AO 80

A. n 72%

ss Improved Heat Exchanger 5.0 (10.0) 10.3 (14.4) 21.3 (19.3) 43.1 (32.5)

Stack Damper 5.5 (11.1) 11.5 (16.0) 23.7 (21.4) 47.8 (36.0)

Direct Vent, (w/preheat) 1.0 (2.1) 2.1 (3.0) 4.4 (4.0) 8.9 (6.7)

Improved Blower (h=65%) -1.6 (50.4) -2.2 (72.0) -3.0 (96.0) -5.0 (161.0)

B. n = 83%

ss Improved Heat Exchanger 4.8 (11.2) 10.0 (16.1) 20.7 (21.6) 41.9 (36.4)

Stack Damper 5.1 (11.8) 10.6 (17.0) 21.9 (22.8) 44.2 (38.4)

Direct Vent, (w/preheat) 0.8 (1.8) 1.6 (2.6) 3.4 (3.5) 6.8 (5.9)

Improved Blower (h=65%)

Independent Analysis

-1.4 (51.0) -2.0 (72.8) -2.6 (97.0) -4.4 (163.0)

A. n ss = 72%

Improved Heat Exchanger 5.0 (10.0) 10.3 (14.4) 21.3 (19.3) 43.1 (32.5)

Stack Damper 5.0 (10.0) 10.3 (14.4) 21.3 (19.3) 43.1 (32.5)

Direct Vent, (w/preheat) 3.8 (7.6) 7.9 (10.9) 16.2 (14.7) 32.8 (24.7)

Improved Blower (h=65%) -2.0 (56.9) -2.9 (81.6) -3.9 (109.0) -6.5 (183.0)

B. h = 83%

ss Improved Heat Exchanger 4.8 (11.2) 10.0 (16.1) 20.7 (21.6) 41.9 (36.4)

Stack Damper 5.7 (13.2) 11.9 (19.1) 24.6 (25.6) 49.7 (43.1)

Direct Vent, (w/preheat) 3.0 (6.8) 6.2 (9.9) 12.7 (13.3) 25.7 (22.3)

Improved Blower (h=65%)

Modified Sequential Analysis

(No Stack Damper)

-1.8 (57.9) -2.6 (83.1) -3.5 (111.0) -5.8 (187.0)

A. n = 72%

ss Improved Heat Exchanger 5.0 (10.0) 10.3 (14.4) 21.3 (19.3) 43.1 (32.5)

Direct Vent, (w/preheat) 3.4 (6.8) 7.1 (9.8) 14.6 (13.2) 29.4 (22.2)

Improved Blower (p=65%) -1.7 (52.2) -2.4 (74.7) -3.2 (99.6) -5.4 (167.0)

b. nss 83%

lnir’- tved Heat Exchanger 4.8 (11.2) 10.0 (16.1) 20.7 (21.6) 41.9 (36.4)

Direct Vent, (w/preheat) 2.6 (6.1) 5.5 (8.8) 11.3 (11.6) 22.9 (19.8)

Improved Blower (t>=65%) -1.5 (53.1) -2.2 (76.0) -2.9 (101.0) -4.8 (170.0)

20
4.4 LIFE-CYCLE COST ANALYSIS OF DESIGN MODIFICATIONS

4.4.1 Calculation Procedures

Once the reduction in annual fuel and electricity consumption has been determined, the savings in annual energy costs (AS) due to a given design modification can be calculated as

AS = (AFC

l - AFC2

) ($/unit

p

) + (AELC

1 - AELC2

) ($/kWh), (4-5)

where AFC-^ and AELC^ = annual fuel and electricity consumption, respectively,

before the modification is installed, and

* AFC2 and AELC2 = annual fuel and electricity consumption, respectively,

after the modification is installed.

However, in order to compare such savings with the additional costs of the

design modifications, they must be adjusted to equivalent savings in total

life-cycle operating costs.

Life-cycle cost analysis is the most appropriate method of evaluating energy

conserving design modifications because all relevant savings and costs incurred over the life of the modifications are considered on a time-equivalent

basis. Time equivalency can be most readily performed by discounting all

future savings (less maintenance and repair costs, if any) to the start of

the useful life of the modifications. These adjusted savings, referred to as "present-value" life-cycle savings, can then be directly compared with the

additional cost of the design modifications in order to determine the cost

effectiveness of the modifications.

While the physical savings from design modifications are assumed to be constant from year to year, the dollar value of those savings is expected to

increase over time because of rising energy prices. A modified version of a uniform present worth factor (UPW) is needed to relate the discounted value

of the increasing dollar savings over the life of a modification to its

annual dollar savings evaluated at the beginning of the first year of use. This modified UPW factor is designated as UPW* to to distinguish it from the more commonly used UPW factor which does not incorporate increasing dollar

savings over time. The derivation of the UPW will be discussed in Appendix A.

In this report both the savings in fuel costs and electricity costs are con- sidered in the life-cycle analysis. Total life-cycle savings (TS), in initial

year dollars, are estimated using

TS = (AFC

1 - AFC2 )($/unitF )(UPWp)

+ (AELC

X - AELC2 )($/kWh)(UPWg)

,

(4-6)

vu_re UPWp and UPWE

= the modified uniform present worth factors for

the heating fuel and electricity, respectively.

(UPWp and UPWE will differ if the expected rate

of price increase for fuel and electricity

differs .

)

21
Any increase in maintenance-related costs due to a design modification must

also be evaluated in present-value terms and added to its initial cost in

order to better estimate the total cost (TC) for that modification. Thus

n TC = IC + E MC

i /(l+D) yi

, (4-7)

i=l

where IC = initial cost

n = expected number of maintenance-related occurences over the

life of the modification,

A. 1_ MC^ = expected cost of the i

1" occurence (base year equals 1),

y^ = year of the i

1"*1 occurence, and

D = discount rate.

If all savings and costs have been properly evaluated, each modification with

present-value life-cycle savings greater than or equal to its total cost is

considered to be cost effective. Conversely, modifications with savings less

than costs are not considered to be cost effective.

4.4.2 Economic Assumptions Used in Analysis

In order to perform a life-cycle cost analysis, appropriate technical performance data and economic data must be selected. The technical performance

data for the gas- and oil-fired furnaces and boilers have already been discussed (tables 2 and 3). A 20-year furnace life is assumed, based on the

data presented by Booz, Allen and Hamilton [1], which in turn was based on a survey conducted of manufacturer representatives, distributors, and heating

contractors. In that report it is assumed that the modifications considered

have equally long lives. Cost data for the modifications are shown in table 1 (projected 1980 dollars), again as estimated by Booz, Allen and Hamilton.

Increased maintenance costs above basic furnace maintenance costs are assumed

to be negligible. (If significant maintenance costs were to be anticipated,

they could be directly incorporated into the analysis by adding them, discounted to 1980 dollars, to the initial costs as illustrated in equation 4-7).

In order to value the annual energy saving in 1980 dollars, 1979 DoE price

projections** of 1980 prices [13] were used for gas and electricity, while

Experience with both the intermittent ignition device and stack damper

indicates that there have been increased maintenance costs associated

with these modifications. It is assumed that newer designs will be more

reliable and therefore need less maintenance. However, at the time of

this writing, no actual projections of maintenance costs are available.

The "Trendlong" economic scenario was used, which assumes a moderate

level of economic growth between 1980-2000.

22
1979 Bureau of Labor statistics (BLS) data [2] were used as the basis for

estimating 1980 fuel oil prices. (Oil price data were taken from BLS because

they better reflected the very significant increase in fuel oil during the

year 1979.) In order to better estimate the minimum dollar savings that

would occur due to the installation of a given modification, energy prices in

the mildest heating climates in the continental U.S. were examined, i.e. the

south and southwest. Then the lowest regional price for each energy type

among these regions was used. Price projections for all three energy types

through the year 2000 are based on the implicit price increase (in real terms)

projected in the DoE report [13] . As a result of this procedure, the following prices and projected real price increases were used:

Energy

Type

Lowest Price

Region

1980

Price

Average Rate of Price

Increase Through 2000 (real)

Gas Southwest $0.30/therm 3.4%

Oil South $1.00/ gallon 3.2%

Electricity South $0. 04/kWh 0.8 %

In order to develop modified uniform present worth factors (UPW*) for each

energy type, a "real" (i.e., after adjustment for inflation) discount rate of

four percent is used in this report. This is approximately equivalent to the

ten percent nominal discount rate (with six percent inflation assumed) used

in similar NBS analyses of air conditioners and insulation in residential

applications. A four percent real discount rate for homeowners implies that

a minimum after-tax, after-inflation annual rate of return on investment of

four percent will be realized from all investments that are cost effective.

However, this rate of return may be considerably higher for investments with

present-value savings significantly larger than costs.

Based on a 20-year life, a four percent discount rate, and the long-term real

energy price escalation rates shown above, the following modified uniform

present worth factors were derived, as explained in Appendix A:

Energy Type UPW*

Gas 18.8

Oil 18.5

Electricity 14.6

4.4.3 Results of Life-Cycle Cost Analysis

A series of economic analyses was performed on the design modifications examined in this report in order to determine the combination of energy price and

heating requirements which make each modification cost effective on a life23
/

cycle basis. Energy savings data are based directly on tables 8 and 9.

Modification costs are from table 1. A range of prices was examined for

natural gas ($0.20 to $0. 40/therm) and oil ($0.80 to $1 .20/gallon) , with the

midpoint equivalent to the estimated 1980 energy prices discussed in section

4.4.2. Electricity costs were held constant at $0. 04/kWh in all cases. However, this is of little consequence except in the analysis of improved blower

efficiency. Note that the rate of price escalation for each energy type (and

thus the modified uniform present worth factors, UPW*) does not vary with

changes in base price assumptions, but remains constant as shown in section

4.4.2.

The cost effectiveness of the IID for a gas-fired furnace or boiler is a function of annual heating hours (AHH) rather than annual heating requirements. Specifically, the savings are directly proportional to (8760

hrs/yr minus AHH). Thus the fewer AHH, the more likely the IID is to be cost

effective. Based on the energy savings shown in table 8 and the $75 cost in

table 1, the IID appears to be cost effective over the entire range of energy

prices and annual heating hours examined. Even at $0.20 per therm and 5000

annual heating hours the life-cycle savings of $132 exceed the first cost of

the modification. As a result, the IID is assumed to be incorporated into

the design of the gas furnace and boiler in all subsequent analyses of design

modifications.* (Note that even with significant maintenance costs the IID

is likely to be cost effective in the majority of applications.)

For all modifications except the intermittent ingition device (IID), the

energy and dollar savings are most sensitive to the annual heating requirements (AHR) . Tables 10 and 11 show the minimum AHR for which these modifications are cost effective, given the fuel prices shown, for gas and oil

furnaces, respectively. That is, at the minimum AHR shown, the present-value

life-cycle (20 years) savings just equal the first costs shown. At any AHR

greater than those shown, the savings exceed costs. The design improvements

shown in tables 10 and 11 are analyzed in two distinct ways, sequentially

and independently.** The sequential analysis begins with the most costeffective modifications and examines the incremental effects of each additional modification in order of decreasing cost effectiveness. The general

ordering of modifications is the same for gas and oil furnaces except that

Present-value savings = (savings in therms)($/therm)(UPW ) gas + (savings in kWh) ( $/kWh) (UPW^^)

= (38.8)($0.20)(18.8) + (-23 .4)($0.04)(14.6) = $132.

Savings in therms and kWh are from table 8, part I.

** In addition, table 11, part III, shows a modified sequential analysis

where the direct venting (with preheat) modification is examined directly

after the improved heat exchanger, leaving out the stack damper. As will

be discussed in section 5.3, odor problems with stack dampers on oilfired units may preclude requiring this latter modification on new units.

24
Table 10. Minimum Annual Heating Requirements3 (in million Btu) for CostEffective Modifications 3

, Gas Furnace

Price Per Therm (Gas)

$0.20 $0.30 $0.40

I. Sequential Analysis

A. 0 = 72%

ss Improved Blower Eff. (@ $. 04/kWh)

Improved Heat Exchanger

Stack Damper

Direct Vent, (w/preheat)

B. 0 =77%

ss Improved Blower Eff. (@ $. 04/kWh)

Improved Heat Exchanger

Stack Damper

Direct Vent, (w/preheat)

II. Independent Analysis

A. n = 72%

ss Improved Blower Eff. (@ $. 04/kWh)

Improved Heat Exchanger

Stack Damper

Direct Vent, (w/preheat)

B. 0 = 77%

ss Improved Blower Eff. (@ $. 04/kWh)

Improved Heat Exchanger

Stack Damper

Direct Vent, (w/preheat)

3 5

9 6

15 10

45 30

3 4

10 7 23 16

50 33

3 5 9 6

17 12

22 15

3 4

10 7 33 23

27 19

7

58

23

6

6

12

25

759

12

6

6

17

15

3 The minimum annual heating requirement is shown for which the corresponding

present -value life-cycle savings at the fuel cost indicated just equals the

total cost of the modification.

k The IID is assumed to be cost effective for all gas-fired systems.

25
Table 11. Minimum Annual Heating Requirements in (million Btu) for CostEffective Modifications: Oil Furnace

Price Per Gallon (Oil)

$0.80 $1.00 $1.20

I. Sequential Analysis

A. ri = 72%

ss Improved Heat Exchanger 3 3 2

Stack Damper 14 11 10

Direct Vent, (w/preheat) 50 40 35

Improved Blower Eff. (@ $. 04/kWh) 25 a b

n _ = 83%

ss Improved Heat Exchanger 3 3 2 Stack Damper 15 12 11

Direct Vent, (w/preheat) 70 53 44

Improved Blower Eff. (@ $. 04/kWh) 12 a b

II. Independent Analysis

A. n = 72%

ss Improved Heat Exchanger 3 3 2

Stack Damper 16 13 11

Direct Vent, (w/preheat) 14 11 10

Improved Blower Eff. (@ $. 04/kWh)

^ss " 83%

60 b b

Improved Heat Exchanger 3 3 2

Stack Damper 13 11 9

Direct Vent, (w/preheat) 18 15 12

Improved Blower Eff. (@ $. 04/kWh) 20 a b

III. Modified Sequential Analysis (No Stack Damper)

A. n = 72%

ss Improved Heat Exchanger

Direct Vent, (w/preheat)

Improved Blower Eff. (@ $. 04/kWh)

B. ri = 83%

ss Improved Heat Exchanger

Direct Vent, (w/preheat)

Improved Blower Eff. (@ $. 04/kWh)

a Dollai. /ings from improved blower efficiency (45% to 65%) are positive

but not large enough to offset higher blower motor cost.

k Dollai savings from improved blower efficiency (45% to 65%) are negative.

3

16

25

3

13

b

2

11

b

3

20

12

3

16

a

2 14

b

26
the improved blower motor modification is analyzed last for oil furnaces

because of its general failure to be cost effective at oil prices of $1.00 or more.* In both the sequential and the independent analysis the IID is

assumed to be installed before any other modification is considered.

Except for the savings due to the IID and blower efficiency improvements,

life-cycle savings for the modifications examined are almost directly proportional to the AHR. Thus, at an AHR twice those shown in tables 10 or 11,

life-cycle savings due to those remaining modifications are double costs.

Efficiency improvements to the blower produce no actual reduction in Btu

consumed at the building site, but rather require a substitution of fossil

fuel for electrical energy so that total furnace output will remain constant.

As a result, dollar energy savings, if any, tend to increase less than proportionally with increases in AHR. Moreover, if life-cycle fossil-fuel costs

exceed life-cycle electricity costs when adjusted to the equivalent Btu output, the savings from improved blower efficiency will be negative. Such

losses occur in table 11 when oil prices equal or exceed $1 .00/gallon, electricity prices equal $0. 04/kWh, and the seasonal furnace efficiency equals or

is less than 77 percent.

In general, the improved blower efficiency modification (i.e., substitution

of a permanent-split capacitor for a shaded pole motor) is cost effective for

gas furnaces when annual heating requirements exceed aproximately five million Btu per year and the price of gas is approximately $0.30 per therm.

Since five million Btu per year is quite low for any house having central

forced-air heating, this implies that a higher efficiency motor is likely to

be cost effective in all installations. However, for oil furnaces the

improved blower efficiency modification is not likely to be cost effective

unless electricity prices are substantially greater than $0.04 per kWh.

The remaining modifications (improved heat exchanger, stack damper, and

direct ventilation air with preheat) tend to be slightly more cost effective

for the lower steady-state efficiency units than the higher steady-state

efficiency units. For gas furnaces, these three modifications are all likely

to be cost effective when AHR exceed 33 million Btu at $0.30 per therm. In

oil furnaces, these same modifications are all likely to be cost effective

when AHR exceeds 53 million Btu at $1.00 per gallon. Using figure 1 as a reference for estimating the magnitude of AHR in a 1200 sq. ft. house, it can

At $1 .00/gallon, UPW* = 18.5 for oil, the present-value 20-year cost

per million Btu output =

1,000,000 Btu

(140,000 Btu/gallon) ( .77)

($1.00)(18.5) = $172.

At $0. 04/kWh, UPW* = 14.6 for electricity, the present-value 20-year

cost per million Btu output =

1,000,000 Btu

(3413 Btu/kWh) (1 .0)

($0.04)(14.6) = $171.

27
be seen that the improved heat exchanger is likely to be cost effective^n all

installations. However, the stack damper and direct ventilation with preheated

air modifications are not likely to be cost effective in smaller houses or tightly insulated houses in the milder climates in the United States. Energy

and dollar savings attributable to gas- and oil-fired boilers are assumed to be

nearly identical to those calculated for the gas- and oil-fired furnaces.

4.4.4 Implications for Outdoor Furnaces and Boilers

The previous subsections have dealt with an economic evaluation of the cost

effectiveness of various design options for furnaces (and boilers) intended for

indoor installation. Another category of central heating equipment which needs

to be considered is that of units intended for installation out-of-doors or in

unheated spaces. This category includes gas- or oil-fired outdoor boilers,

outdoor furnaces and horizontal furnaces.

Unlike indoor boilers and furnaces, the DoE test procedure requires that the

seasonal performance of outdoor units be reduced by their estimated jacket

losses at an average winter outdoor (attic or crawl space) temperature of 42°F.

The procedure employed tends to assign boilers a slightly larger jacket loss

than furnaces* due to their generally higher mass and longer off-times and

tends to show horizontal and outdoor furnaces as having slightly less efficient heat exchangers than their indoor, upflow and downflow conterparts.**

Consequently, outdoor boilers and furnaces (including horizontal furnaces)

both tend to have seasonal efficiencies which average between three and five

percentage points below comparably equipped indoor units having the same steady-state efficiencies. As a result, the IID and improved heat exchanger

design options which were shown previously to be cost effective for most

indoor units are even more cost effective for outdoor boilers and furnaces.

Stack dampers and preheated combustion air modifications, on the other hand, are not applicable to outdoor units because these units either do not employ

draft diverters, draft hoods or barometric draft regulators*** or do employ

these devices but use unheated outdoor air for draft control. The installation of a stack damper would serve no useful function on the latter type

* The jacket loss coefficient (C^) assigned in the DoE test procedure

is 4.7 for boilers and 3.3 for furnaces.

** This is believed to be due to a slightly higher mass per Btu/h input

and a lower height to depth ratio.

*** The DoE test procedure defines a stack damper as an automatic damper

"installed downstream of the integral draft diverter, draft load or baromatic draft regulator." The application of a flue damper, which

is an automatic damper installed upstream of the draft control device

or vent terminal (on units not equipped with a draft control device),

is not considered in this report because it is uncertain whether

such devices save energy when installed on outdoor units and because

the various associations concerned with safety have not yet approved

the use of such devices on outdoor furnaces and boilers.

28
units since heated air passing through the heat exchanger during the offperiod would simply exit through the draft relief opening and be lost.

5. IMPLICATIONS FOR STANDARDS DEVELOPMENT

5.1 AN ECONOMICALLY OPTIMAL STANDARD FOR CONSUMERS

The analysis conducted for this report suggests that a standard which

requires the same level of fuel-utilization efficiency for all furnaces and

boilers of a given type in the United States would not be the most costeffective standard possible. This is because some modifications to furnaces

and boilers, particularly the stack damper and direct venting with preheated

combustion air, were found to be cost effective only in installations with

substantial annual heating requirements, not typical of smaller houses or tightly insulated houses in the milder regions of the U.S. As a result, if

these two modifications are required in all new furnaces, consumers in such

houses will not recoup the increased cost of the modifications. On the other

hand, if these two modifications are not required, they will not be installed

in many houses where they are clearly cost effective on a life-cycle cost

basis.

A standard which requires that a furnace or boiler achieve a given minimum

level of efficiency can be made more cost effective if it requires higher

efficiency levels only where those higher levels can be achieved at a cost

less than or equal to the life-cycle savings in energy costs. Thus, a flexible standard could be developed which would link the performance requirements of a new furnace or boiler to the annual heating requirements of the

building in which it is to be installed. Such a standard could be better

implemented through the local building code authority than through equipment

manufacturers

It is unlikely that such a flexible standard will be adopted, however,

because the legislation requiring minimum standards for central heating

equipment imposes them on the manufacturer rather than the end user. Since

the manufacturer has little control over the shipment of his units, this is

tantamount to requiring the same minimum efficiency for all units produced.

This, of course, is contrary to the principle of economic differentiation

advocated above.

5.2 A PRACTICAL STANDARD FOR MANUFACTURERS

A compromise standard is possible, however, which retains some ability to

differentiate among end uses while allowing the standard to be imposed on

the manufacturer rather than the end user. Figure 2 shows a rough relationship between annual heating requirements and minimum design heating load,

* To the extent that such a problem can be attributed to a failure in

consumer marketplace behavior, other mechanisms besides mandatory

standards could be used to correct this situation. However, this is

outside the scope of this report.

29
based on figure 1. That is, for any given design heating load on the horizontal axis the corresponding AHR is likely to be at least as great as, if

not greater than, that shown on the vertical axis. Using this relationship

and an appropriate oversizing ratio, a minimum performance standard could be

differentiated according to the output capacity of a furnace or boiler,

rather than annual heating requirements. As a result larger furnaces or boilers would have higher efficiency requirements than smaller furnaces or boilers. By using energy prices which are representative of the region in

which the modifications are likely to be marginally cost effective, this

methodology will generally result in minimum standards which can be lifecycle justified in the majority of applications.

Table 12 provides a list of the design modifications examined in this report

and the annual heating requirements needed to make them cost effective at the

energy prices shown for gas- and oil-fired furnaces and boilers. The energy

savings implicit in this table are based on the lower efficiency (i.e., 72

percent steady-state efficiency) units analyzed, since these units, modified

as indicated, will likgly serve as the base point for calculating minimum

performance standards. In addition, table 12 shows the corresponding design

heating loads (based on figure 2) and output requirements (assuming an oversizing factor of 1.7). While this table is prescriptive in nature, minimum

standards corresponding to these configurations could be formulated in performance terms, using seasonal fuel utilization efficiency as the performance

measure. The seasonal fuel utilization efficiencies thus employed should be

based upon experimental data obtained using the Department of Energy's

furnace test procedure [5]

.

5.3 OTHER CONSIDERATIONS IN SETTING STANDARDS FOR FURNACES AND BOILERS

Design modifications required (either implicitly or explicitly) in setting a minimum efficiency standard must, in addition to being cost effective, meet

other criteria outlined in section 2. One of these criteria is that the

standard does not cause a major disruption of the industry. A design option

which may not meet this requirement is direct venting with preheating of

incoming combustion air on indoor furnaces and boilers. Even though Booz,

Allen and Hamilton [1] gave the price of this design option as only $85, its

implementation requires a major redesign of a furnace or boiler. While a manufacturer might be willing to do this on a number of models in his manu- facturing line, it is not reasonable to expect him to redesign all of his

units unless a reasonably long lead time is given. Since it has been shown

that direct venting with preheating is the least cost-effective design option

examined, it is important that the number chosen for the furnace or boiler

minimum performance standard not be set so high as to require this major

design modification for all new residential, indoor, central heating equipment in the near future.

jl .

>

section 3.2, an efficiency of 72 percent was selected to bracket, on

the low side, the steady-state efficiency of both gas and oil furnaces

,nrl boilers.

30
Table 12. Furnace/Boiler Output Capacities Corresponding to Annual

Heating Requirements 3

Annual

Heating

Requirements*5 (106 Btu)

Design

Heating

Load

(103 Btu)

Furnace/

Boiler

Output 0

(103 Btu)

I. Gas Furnace/Boiler

Modifications:

(1) Improved Heat Exchanger 6 17 29

(2) Stack Damper 10 23 39

(3) Direct Vent, (w/pre’neat) 30 40 68

Oil Furnace/Boiler

(1) Improved Heat Exchanger 3 13 22

(2) Stack Damper 11 24 41

(3) Direct Vent, (w/preheat) 40 45 77

a For a given furnace or boiler output that is properly sized, the annual

heating requirements are likely to be at least as great as shown, based

on curve shown in figure 2. Based on sequential analysis of modifications, with IID used in all cases.

k From tables 10 and 11 for the 72% steady-state efficiency units.

c Output = design heating load x 1.7 (oversizing factor).

31
A second criterion which must be met by a minimum standard is that it does

not force unsafe, unreliable, and unacceptable products on the consumer. A

design option which may give unacceptable performance is the installation

of stack dampers on indoor oil-fired furnaces and boilers. A recent study

involving the installation of stack dampers on 23 existing oil-fired furnaces and boilers in the New England area [8] resulted in odor problems in

11 installations and eventual disconnection of eight (35 percent) of the

devices for this reason. Although this was a retrofit study, the burners,

furnaces and boilers were representative of those presently being manufactured and there is no reason to believe that this problem could not also

exist for new equipment. Based upon this uncertainty, it is recommended

that for the present time minimum performance standards for oil -fueled fur- naces and boilers be set at a level which does not require manufacturers to

install stack dampers on oil-fired equipment. The normal incentives of high

fuel costs and appliance labeling as well as the performance nature of the

standards should encourage manufacturers to incorporate this design option

on many of their indoor units as the odor problem is solved. If this occurs without significant problems, minimum standards for oil-fired furnaces and

boilers could then be raised to reflect the use of stack dampers on this

_ . * type of equipment.

A third criterion is that all minimum standards must be based upon results

obtained using DoE test procedures [5]. However, the use of improved blower

motors on gas furnaces cannot be factored into a minimum efficiency standard

for furnaces based on these procedures. While the electrical energy consumed

(and the heat given off) by a furnace blower is used in the test procedure to

determine the annual operating cost, it does not enter into the calculation

of the seasonal efficiency number. This was done to prevent manufacturers

from trading off increased operating costs (and total resource energy con- sumption) for a higher seasonal efficiency number. This situation could best

be corrected by DoE modifying its present definition of seasonal efficiency

from one based upon onsite fuel consumption to one based upon resource energy

requirements (sometimes referred to as "energy at the coal pile") or to one based on cost weighting factors for the different energy types used. If this

is not possible, an alternative solution is proposed in section 6 which could

achieve many of the same benefits.

Evaluating the life-cycle cost study results summarized in section 4.5.1, in

light of these three criteria, leads to the conclusion that only the following design modifications should be considered in setting minimum performance

standards:

1) an IID on both indoor and outdoor gas-fired units (oil-fired units

already incorporate this design option)

,

It should be noted that the direct venting (with preheat) option is

likely to be cost effective on all oil furnace and boiler systems

if the stack damper is not used. However, the major design changes

required for this modification weigh against its immediate incorporation into the proposed minimum standard.

32
2) an improved heat exchanger on all indoor and outdoor furnaces and

boilers (corresponding to five percentage points increase in steadystate efficiency), and

3) the use of stack dampers on indoor gas-fired furnaces and boilers

with output capacities equal to or greater than 40,000 Btu/h.

Manufacturers would, of course, be free to achieve this minimum level of

performance by whatever means possible (such as by using power burners,

direct venting with preheating of incoming combustion air, etc.)*

5.4 TECHNICAL BASIS FOR STANDARDS SETTING

5.4.1 Gas Furnaces and Boilers

An analysis of data presented by the Gas Appliance Manufacturers Association

(GAMA) [7] reveals that, with the exception of one gas furnace, the lowest

steady-state efficiencies measured by GAMA for current production models of

gas furnaces and boilers was approximately 72 percent. A five percentage

point improvement in the steady-state efficiency, due to an improved heat

exchanger, would increase this steady-state efficiency to 77 percent. An NBS

technical analysis of gas furnaces [11], based on the DoE furnace test procedure and thought currently to be the most reliable summary of results

obtained using this procedure, shows that a steady-state efficiency of 77

percent corresponds to an expected seasonal efficiency of 68 percent for gasfired furnaces and boilers equipped with HD's and an expected seasonal efficiency of 74 percent for gas-fired indoor furnaces and boilers equipped with

both I ID's and stack dampers.

Relating seasonal efficiency and steady-state efficiency for gas-fired outdoor

units is considerably more difficult because of the limited amount of data

available on these systems. The best approach appears to be to adjust the

average seasonal efficiency of 68 percent, found for indoor units equipped

with an IID and having a steady-state efficiency of 77 percent, for the

effect of jacket losses and for the reduced heat exchanger effectiveness

of outdoor (including horizontal) furnaces. Assuming a typical jacket loss

of 0.75 percent on a well insulated furnace or boiler tested in the laboratory, the seasonal jacket loss (as calculated in the DoE furnace test procedure) becomes (0.75x3.3 =) 2.5 percent for outdoor furnaces and (0.75x4.7=)

3.5 percent for outdoor boilers. If a value of 2.0 percentage points is

assigned to account for reduced heat exchanger performance,* it is concluded

that an outdoor furnace with a steady-state efficiency of 77 percent is

likely to have a seasonal efficiency of approximately (68-2.5-2=) 63.5 percent. Subtracting the seasonal jacket loss for outdoor boilers from 68

This is perhaps the weakest point in the argument. It is based upon the

test of a single unit at NBS and data contained in a draft report by AGA

laboratories [6]

.

It is suggested that when DoE proposes minimum standards

they also request manufacturers to provide actual test data on horizontal

units tested according to the DoE test procedure.

33
percent yields a seasonal efficiency of approximately 64.5 percent. Within the accuracy of this analysis, it would appear that a seasonal efficiency

of approximately 64 percent might reasonably be expected from both outdoor

furnaces and boilers having a steady state efficiency of about 77 percent

and employing an intermittent ignition device (IID).

Based upon these results and the fact that minimum standards give the lowest

levels of acceptable performance, the following minimum performance standards

for gas-fired, residential, central heating equipment appear to be generally

cost effective and compatable with the criteria for standards development

detailed in section 2.

Table 13. Minimum Seasonal Efficiencies for Gas-Fired Central Heating

Equipment

Minimum Seasonal Efficiency As

Type of Heating Equipment Measured Using the DoE Furnace

Test Procedure [5]

Cas-t Lr. .1 indoor furnaces and

indoor hollers with output 68%

apnoitius he Low 40,000 Btu/h

Gas-fired indoor furnaces and

indoor boilers with output

v-apa. Lties equal to or greater 74%

than 40,000 Btu/h

Gas-fired outdoor furnaces

and outdoor boilers 64%

The above minimum standards for gas-fired units should assure that most of

the gas-fired indoor units presently being manufactured would be required

to have a seasonal efficiency at least as high as a low efficiency furnace/

boiler equipped with an IID, an improved heat exchanger and a loose stack

damper. In addition, the development and production of small capacity

indoor units would not be hindered by forcing them to be equipped with a design option (e.g. stack damper) which may not generally be cost effective.

5.4.2 Oil Furnaces and Boilers

The lowest steady-state efficiency reported for oil-fired furnaces and boilers

by GAMA is approximately 75 percent [7]. A five percentage point increase in

this steady-state efficiency due to an improved heat exchanger would result

in a steady-state efficiency of 80 percent.

34
NBS technical analysis of furnaces [11], based on the DoE test procedure,

shows that a steady-state efficiency of 80 percent corresponds to an expected

seasonal efficiency of approximately 76 percent for the oil-fired indoor furnaces and boilers tested. For oil-fired outdoor units, the same type of

analysis that was carried out for gas-fired outdoor units yields a seasonal

efficiency of approximately 73 percent if a typical laboratory measured jacket

loss of 0.75 percent is assumed and the effect of reduced heat exchanger

effectiveness on outdoor furnaces is taken to be one be one percentage point.*

Based upon these results, the following minimum performance standards for oilfired residential heating equipment are generally cost effective and consistent with the criteria for standards development outlined in section 2.

Table 14. Minimum Seasonal Efficiencies for Oil-Fired Central Heating

Equipment

Minimum Seasonal Efficiency As

Type of Heating Equipment Measured Using the DoE Furnace

Test Procedure [5]

All oil-fired indoor furnaces

and indoor boilers 76%

All oil-fired outdoor furnaces

and outdoor boilers 73%

It is recommended that this minimum seasonal efficiency number be revised

upward to 80 percent** for oil-fired indoor furnaces and boilers with output

capacities equal to or greater than 40,000 Btu/h, if at a later date it is

determined that the addition of stack dampers to this type of indoor equipment does not cause insurmountable odor problems.

Finally, it is recommended that any minimum efficiency numbers adopted by the

Department of Energy be periodically subjected to review and that they be

revised as energy costs, modification costs, product lines and installation

practices change.

* A value of one percentage point was used instead of two percentage

points, because the difference between the steady-state and seasonal

efficiencies shown for oil-fired units are approximately half that

shown for gas-fired units.

** This gives a seasonal efficiency equal to the steady-state efficiency.

To require a higher seasonal efficiency as a result of installing a stack

damper could be unfair to oil-fired furnaces and boilers with lightweight

heat exchangers.

35
6. AN ALTERNATIVE METHOD FOR SPECIFYING MINIMUM BLOWER MOTOR EFFICIENCY

It was mentioned previously that while the use of high efficiency blower

motors on gas furnaces was justified economically, this design option could

not be used in setting minimum efficiency standards for furnaces because the

DoE seasonal efficiency calculation did not account for the auxiliary electrical energy consumed by fossil-fuel-fired central heating equipment. One

alternative which would allow both the consumer and the country to benefit

from the resource energy saved by using more efficient blower motors is for

DoE to change its definition of furnace annual efficiency to account for the

electrical energy used. A second alternative would be, for each category

of furnace, to have two minimum efficiency standards: one based on the data

base developed in section 5 for the annual fuel utilization efficiency and a second specifying the minimum allowable blower motor efficiency. In the

event that DoE wishes to avail itself of the latter alternative, the following efficiency data for consideration in the development of minimum performance standards for furnace blower motors has been provided:

Table 15. Minimum Efficiencies for Furnace Blower Motors

Motor size (HP)

1/7 < HP < 1/5 50%

1/5 < HP < 1/3 55%

HP > 1/3 60%

These are based on the data shown in figure 3 for the typical spread currently

found in the efficiency of permanent-split capacitor (P.S.C.) and shaded pole

(S.P.) motors. The data was supplied by a leading manufacturer of furnace

blower motors. The solid step-like line in figure 3, which represents the

above referenced minimum efficiencies for furnace blower motors, would force

manufacturers to switch from S.P. motors to more efficient and more costeffective P.S.C. motors.

Blower motor efficiencies should be measured in accordance with IEEE Standard

114 (Test Procedure for Single-Phase Induction Motors) with the motor operating at full load or at the high speed connections. This information should

be readily available from the blower motor manufacturer and no testing or verification of motor performance should be required of the furnace manufacturer.

i

7 . CONCLUSIONS

The National Energy Act of 1978 requires that the Department of Energy (DoE)

develop minimum performance standards for new residential gas- and oil-fired

furnaces and boilers produced in the U.S. This report examines available

36
I

70

/

/

/

Typical spread in

P.S.C. motor efficiencies

/

>-O

60 - /

uj 50 -

40 -

/

/

/

/

/

//

/ Typical spread in S.P. motor efficiencies

V *

/

30 - /

/

7

'e Recommended minimum

motor efficiency level

/ A

/

/

/

/

/

J I L i

1/8 1/6 1/4 1/3 1/2 3/4

HORSEPOWER RATING

Figure 3. Typical P.S.C. and S.P. motor efficiencies and suggested minimum

motor efficiency level (data on typical motor efficiencies supplied

by a leading manufacturer of furnace blower motors)

37
technological improvements to such systems in order to determine which are likely to be cost effective from a consumer standpoint and implementable

without serious disruption to the industry. Performance data, in terms of

seasonal conversion efficiencies, are then identified which correspond to

basic furnace and boiler systems incorporating those improvements. These

specifications can be used as the basis of minimum performance standards that are life-cycle-cost justified in the majority of applications.

The following conclusions are specifically forthcoming from this report:

(1) The intermittent ignition device for a gas furnace is likely to

be cost effective in all installations when compared to the

annual cost of a standing pilot light.

(2) An improved heat exchanger (five percentage points above the

steady-state efficiency of the base case models identified in

this report) will likely be cost effective in all gas- and

oil-fired central heating equipment.

(3) The cost-effectiveness of a stack damper is largely related to

the magnitude of the annual heating requirements of the building

in which the furnace/boiler is installed. In houses with relatively small annual heating requirements, the stack damper is

not currently cost effective in many cases.

However, for larger houses and houses in colder climates the

stack damper is generally cost effective on a life-cycle basis.

As a result, stack dampers are found to be generally cost effective for indoor gas furnaces and boilers with output capacities

above 40,000 Btu/h. Odor problems associated with stack dampers

in oil furnaces and boilers suggest that this modification is

not presently suited for general use in these latter systems

until this problem is eliminated. Stack dampers do not appear

to reduce energy usage significantly when used in outdoor units.

(4) Direct outdoor venting with preheated air appears to be life-cycle

cost effective primarily in houses with relatively large heating

requirements, making this design modification practical for most

indoor gas furnaces and boilers with output capacities above

approximately 68,000 Btu/h and for most indoor oil furnaces and

boilers above 77,000 Btu/h if a stack damper is used as well.

If a stack damper is not used, the external ventilation with

preheated air will also be cost effective on somewhat smaller

equipment. However, if direct venting with preheated air is made

mandatory, a major disruption of the industry is likely to result,

since major design changes would be required of virtually all new

furnaces and boilers. As a result, this modification is not

suggested as a feature to be implicitly included in the perfor- mance standard. Because of the nature of the performance standard,

however, manufacturers can take credit for incorporating this

feature into new furnace designs as new equipment lines are produced

38
(5) Improved heat exchangers and intermittent ignition devices

appear to be cost-effective modifications to furnaces and

boilers installed outside of the conditioned space. However,

the stack damper and preheated ventilation air modifications

do not add significantly to the seasonal efficiency of these

units and thus are not likely to be cost effective.

(6) Minimum performance levels for gas and oil furnaces and boilers

corresponding to the above analysis can be stated as follows:

Seasonal Efficiency

Furnace/Boiler Type Gas Oil

Indoor Units

1. Units with less than

40,000 Btu/h output 68% 76%

2. Units with 40,000 Btu/h

output or greater 74% 76%

Outdoor Units (all) 64% 73%

(7)

While some improvement in the efficiency of the blower motor

for furnaces appears to be quite cost effective for gas furnaces, this improvement cannot be directly factored into a performance standard based on the DoE test method. Thus a separate performance standard for blower motor efficiency may

be advisable.

In addition to these conclusions, it should be recognized that much of the

performance data utilized in this report is based on either limited testing

or simulated results. Additional measured data on performance improvements

related to design modifications would be of considerable help both in

improving the standards development process and in determining the extent

to which the modifications examined will enable the manufacturer to most

economically comply with the standards as they are promulgated.

39
REFERENCES

1. Booz, Allen and Hamilton, Inc., Energy Efficiency Program for

Appliances: Furnaces, Home Heating Equipment, Humidifiers , Volume II, October 1977.

2. Bureau of Labor Statistics, "Consumer Prices: Energy", USDL-80-111,

Washington, D.C., January 1980.

3. Chi, J., Kelly, G. and Didion, D., "Use of a Computer Model to Evaluate

Energy Savings Potentials for Gas-Fired Furnaces," Paper #78-IHTC-77

given at 1978 International Heat Transfer Conference, Toronto.

4. Department of Energy, "Energy Conservation Program for Consumer Products,"

Federal Register , Vol. 44, No. 1, January 2, 1979.

5.

Department of Energy, "Test Procedures for Furnaces and Vented Home

Heating Equipment," Federal Register , Vol. 43, No. 91, Wednesday,

May 10, 1978, pages 20108 through 20205.

6. DeWerth, D. W. , "Evaluation of the Proposed DoE Efficiency Rating

Procedures for Furnaces," Draft report sponsored by the Gas Appliance

Manufacturers Association and the American Gas Association Laboratories,

January 1978.

7. Gas Appliance Manufacturers Association (GAMA), memo to Efficiency Task

Group of the Furnace and Boiler Division, November 23, 1977

(unpublished)

8. Katzman, L., Kelly, George E. and Kuklewicz, Mark E., "An Assessment of

Retrofitting Automatic Vent Dampers on Oil-Fired Residential Heating

Systems in the New England Area,” 1978 HVAC Equipment and Systems Conference, Purdue University, October 23-25, 1978.

9. Kelly, G. , Chi, J. and Kuklewicz, M. , Recommended Testing and Calcula - tion Procedures for Determining the Seasonal Performance of Residential

Central Furnaces and Boilers , NBSIR 78-1543, National Bureau of Standards,

March 1978.

10. National Bureau of Standards, "Appliance Energy Efficiency Improvement

Target - Furnaces," Letter Report to Department of Energy, September 1,

1977.

11. National Bureau of Standards, "Technical Analyses of Public Hearing

Testimony Regarding Proposed Energy Efficiency Improvement Targets

for Furnaces," Letter Report to Department of Energy, March 23, 1978.

12. Petersen, Stephen R., Economics and Energy Conservation in the Design

of New Single-Family Housing , NBS Building Science Series, in review.

13. Sitzer, Moden and DonVito, Historical and Forecasted Energy Prices by

DoE Region and Fuel Type for Three Macroeconomic Scenarios , DoE/EIA0184/15, Department of Energy, Washington, D.C., 1979

14. Stamper, E., "Weather Data," ASHRAE Journal, February 1977, p. 47.

40
APPENDIX A

) DERIVATION OF MODIFIED UNIFORM PRESENT WORTH FACTORS

One of the most critical aspects of a life-cycle cost analysis is that of

evaluating a flow of future benefits or costs associated with some design

change in present-value terms. In general, this requires that future

benefits or costs be discounted to present value using an appropriate

discount rate. ^The purpose of this appendix is to show the derivation

of the modified uniform present worth (UPW*) factors used to evaluate

the present value of the energy savings over the life of the modifications

examined.

Dollar-valued energy savings can be calculated for each year over the life

of a design modification and discounted to present value. However, if the

physical energy savings are assumed constant from year to year, it is

generally easier to calculate a modified uniform present worth factor

which, when multiplied by the annual energy savings calculated at the cost

of energy in the initial time period, will produce the same results.

That is:

present value annual price of energy

life-cycle = UPW x energy x at initial time

savings savings period

The UPW* factor is a function of the life over which the savings are expected to be realized, the discount rate, and the rate at which energy

prices are expected to increase over the life of the modification. A 20-

year life and a four percent real discount rate (i.e. four percent above

the rate of inflation) are assumed in this report, as discussed in section

4.4.2. The rate of energy price increase for each type of energy examined

(gas, oil, and electricity) is derived from the DoE energy price projections

[ 12 ].

If the discount rate and the rate of energy price escalation are constant

over the life of the modifications, the modified uniform present worth

factor can be calculated using:

UPW* = I

f L±_Lfc

> (A— 1)

t=l 1 + D

The term "modified" is used to describe a uniform present worth factor

which incorporates an increasing cash flow over time rather than a conventional UPW factor which is based on a constant cash flow over

time.

A-l
where L = the lifetime of the modification (in years),

P = the annual rate of price increase for energy, and

D = the discount rate.

Note that if P = D, the increase in fuel prices just offsets the

discount rate so that the UPW is equal to the lifetime in years, i.e.,

the savings are simply added each year at initial year energy prices.

If P does not equal D, equation A-l can be reformulated as:

UPW* - ( 1 + P

D - P

-) d-( 1 + P>.L

1 + D

; ). (A-2)

Based on the real rates of fuel and electricity price increase derived

in section 4.2.2, a four percent real discount rate and a 20-year equipment life, the UPW factors used in the report were calculated as follows:

Gas: P = 3.4%

UPW* = ( 1 -

-

.QjA.)

( i - ( 1 . -Q34) 20

) = 18 .8

0.006 1.04

Oil: P = 3.2%

UPW* = ( 1,Q 32)

( 1 - ( L-P.32) 20

) = 18.5

0.006 1.04

Electricity: P =

UPW* , 1.008

4.032-)d

0 . 8 %

, 1^008. 20

4.04 ; ; 14.6

A-2
APPENDIX B

EXPLANATION OF DESIGN MODIFICATIONS TO FURNACES/BOILERS*

Power Burner (or Induced Draft or Forced Draft)

The installation of a fan for supplying combustion air or for force venting

the products of combustion tends to reduce the off-period losses and, thus,

improve a unit's seasonal efficiency. The fan can be installed ahead of the

combustion chamber (forced draft) or after the combustion chamber (induced

draft.

)

Fuel and Air Modulation

The magnitude of off-cycle losses can be reduced by increasing system ontime and reducing the rate of fuel input to the furnace or boiler. However,

a simultaneous reduction in combustion air provided to the burner to avoid

large excess air ratios must accompany the reduction in fuel input in order

to avoid adverse affects on system efficiency. Fuel input can be modulated

in discrete steps or continuously, but is limited at the lower end due to

considerations for condensation and flame stability.

Automatic Stack Damper (Vent Damper)

The presence of a vent system and chimney on a conventional furnace significantly reduces the seasonal efficiency of these appliances. Immediately after

the termination of combustion, the heat stored in the heat exchanger provides

a driving force which causes a flow of air through the exchanger and up the

chimney. This flow carries with it whatever heat remains in the exchanger

after the circulating air blower is switched off. In addition to causing

heat exchanger cool down, the exfiltrated air (including air passing through

the draft control devices) must be made up by increased infiltration of cold

air into the house. The installation of an automatic damper in the vent pipe,

downstream of the draft diverter or draft regulator, can significantly reduce

the volume of this flow.

Intermittent Ignition Device (Electric Pilot)

Ignition of the main burner in a gas-fired heating system has traditionally

been accomplished by using a standing, or continuously burning, pilot light.

During the non-heating season, the fuel consumed by the pilot is wasted.

This loss reduces the annual efficiency of the appliance. Replacement of the

standing pilot with an intermittent ignition device has the potential, therefore, of decreasing energy consumption. The IID ignites by spark ignition

either the main burner directly or a pilot flame.

Based on Booz, Allen and Hamilton, Inc., "Energy Efficiency Program

for Appliances, Furnaces, Home Heating Equipment, Humidifiers [ 1]

.

B-I
Direct Venting (with preheated air)

A standard furnace, installed in an indoor location, uses conditioned air for

both combustion and draft control. This air, which is exfiltrated from the

house through the chimney, increases the amount of cold air infiltrated into

the house from the outside. The necessity of having to heat this air to

indoor conditions results in a loss of efficiency for the system. The loss can be eliminated by sealing the combustion chamber from the area in which

it is installed and bringing combustion air in from the outside through a suitably designed vent. In order to improve the seasonal efficiency of the

appliance, the vent/air intake system should be designed to use the existing

hot flue gas to preheat the incoming combustion air.

Improved Heat Exchanger

The steady-state efficiency of conventional furnaces is governed primarily by

the effectiveness of the heat exchanger. A 5 percentage point increase in

steady-state efficiency, up to 80-82 percent, can be achieved by increasing

the size of the heat exchanger with respect to the burner firing rate, or by

reducing the firing rate and keeping the heat exchanger size and the excess

air ratio constant.

High Efficiency Blower Motor

The upgrading of blower motor type from the conventional shaded pole motor

used in most furnaces in the mid 1970's to a permanent -split capacitor type

motor would represent approximately 30 percent less consumption of electricity. The permanent-split capacitor motor with its extra windings and run- ning capacitor achieves the same horsepower while consuming less electricity.

B-2
NbS-lUA (REV. ®*7B)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSIR 80-2079

on No,

,

I!: ft:

4. TITLE AND SUBTITLE

An Economic Analysis of Efficiency Improvements to

Residential Gas-and Oil-Fired Central Heating Equipment

S. Publication Date July 1980

Organization Code

7. AUTHOR(S)

Stephen R. Petersen, George E. Kelly

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

10. Project/Task/Work Unit No. 742 2506

11. Contract/Grant No.

12. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, City, state, ZIP)

Department of Energy

20 Massachusetts Ave., N.W.

Washington, D.C. 20585

13. Type of Report & Period Covered

Final

15. SUPPLEMENTARY NOTES

| | Document describes a computer program; SF-185, FIPS Software Summary, is attached.

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant bibliography or

literature survey, mention it here.) Minimum performance standards for new residential gas- and oil-fired furnaces and

boilers will be promulgated by the Department of Energy in the early 1980’s. These

standards will implicitly require that a number of design modifications be made to

improve the seasonal efficiency of many basic furnace/boiler configurations. This

report examines the potential improvement in seasonal efficiency due to a number of

such modifications, as well as their life-cycle cost effectiveness. Included in the

analysis are intermittent ignition devices (for gas-fired equipment), improved heat

exchangers, stack dampers, external venting (with preheated air), and improved blower

motor efficiencies (for forced-air furnaces). NBS DEPAF simulation data, the DOE/NBS

furnace and boiler test procedures, current estimates of modification costs, and a wide range of annual heating requirements and fuel costs are used in the analysis.

Minimum efficiency criteria for new furnaces and boilers are developed, based on the

estimated performance of current configurations representative of lower efficiency

models, upgraded with those energy-saving modifications which are generally cost

effective and can be implemented without serious disruption in the industry.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name;

separated by semicolons)

Boilers; central heating equipment; economic analysis; furnaces; incremental savings;

life-cycle costs; minimum efficiency levels; minimum efficiency standards.

18. AVAILABILITY [X] Unlimited

| | For Official Distribution. Do Not Release to NTIS

I | Order From Sup. of Doc., U.S. Government Printing Office, Washington, DC

20402, SD Stock No. SN003-003-

Order From National Technical Information Service (NTIS), Springfield, VA. 22161

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